The present invention relates to a method of transmitting a virtual container of a synchronous transfer mode by using a network of an asynchronous transfer mode.
As a conventional method of transmitting signals of a synchronous transfer mode by using a network of an asynchronous transfer mode, there has been known a method of dividing a bit stream per one cell size to transmit the bit stream thus divided as described in Watanabe etc., "A realization of adaptation for continuous bit rate communication in a ATM network", National Convention of The Institute of Electronics, Information and Communication Engineers of Japan, March 1990, Paper B-457. In this method, a bit stream is transparently transmitted independently of the frame structure of information. Boundaries between frames of the bit stream are discriminated by using frame synchronization patterns inserted in the bit stream.
In the synchronous digital hierarchy prescribed in CCITT (International Telegraph and Telephone Consultative Committee) Recommendation G.709, a virtual container having multiplexed information is mapped onto a transmission frame and transmitted. In this case, the boundary or first bit position of a virtual container within a transmission frame is indicated by using a pointer which is a frame phase identifier fixedly arranged in the transmission frame. That is to say, the boundary of the frame of a virtual container is given in the synchronous digital hierarchy of G.709 by the relative relation with respect to the transmission frame instead of the frame synchronization pattern. In case no transmission frames are present, the boundary of the frame must be discriminated by some other method.
The case where virtual containers are transmitted by using a network of an asynchronous transfer mode is also one of examples in which transmission frames of a synchronous digital hierarchy are not used. In a system in which a bit stream is transparently transmitted such as the above described conventional method, the boundary of the frame of a virtual container cannot be discriminated on the receiving side. Further, a method of providing the boundary of the frame of a virtual container with a frame synchronization pattern in dividing a virtual container into cells of an asynchronous transfer mode can be easily considered. In this method, however, alteration of size of a virtual container and rapid alteration of a virtual container using a new data flag, which are features of the pointer of the synchronous digital hierarchy, cannot be made.